Basic Concepts

The subject of the "spin" of the electron comes up again and again, so as pointed out in a comment, I really ought to do a post explaining what it is and how it works. As a bonus, this gives me the opportunity to do the dorkiest thing anyone has ever done with a cute-toddler video, namely this one: (That's an early version of SteelyKid's new favorite game. I'll put a clip of the final version of the game at the end of this post.) So, electron spin. Electrons, and all other fundamental particles, have a property known as "spin." This is an intrinsic angular momentum associated with the…

On Thursday last week, the Schenectady weather forecast I have in my Bloglines feed called for "Tons of Rain," which I thought was amusingly unprofessional. I mentioned this to Kate yesterday (after it had, in fact, rained quite a bit), and she said "I wonder how much rain you would need to make a ton?" Being a physics nerd, of course I had to try to come up with an answer. We know that one cubic centimeter of water has a mass of one gram, so a (metric) ton of water would be 1,000,000 cubic centimeters, or one cubic meter. Our yard is about 20m x 50m, so if rain covered our yard to a depth of…

One of my tasks this week, before heading off to the Caribbean for a relaxing vacation, is going to be to find a new pair of polarized sunglasses that aren't ridiculously ugly. This seems like a decent hook of a physics post, explaining why "polarized" is a selling point for sunglasses, but first, I probably ought to explain what we means when we talk about the polartization of light. As you know, even if your name isn't Bob, light can be thought of as an electromagnetic wave. You have an electric field oscillating in space and time, and a magnetic field with it, oscillating at the same…

Closely related to the idea of order-of-magnitude estimates is the idea of Fermi Questions, a type of problem that demonstrates the power of estimation techniques. The idea is that you can come up with a reasonable guess at an answer for a difficult question by using some really basic reasoning, and a few facts here and there. The classic example of a Fermi Question is "How many piano tuners are there in Chicago?" This has never really worked for me, though, because I don't know anything about pianos, and I have no real way of knowing how often they're tuned, or any of the other estimates. So…

Ages and ages ago, Jennifer Ouellette commented on the start of the Basic Concepts series with a list of topics she'd like to see done. One of these was "Size and Scaling:" First, let's tackle the jargon problem: Just what the heck is an order of magnitude? I use the phrase all the time now, after years of hanging around physicists, but as a budding science writer, I found the term a bit opaque, and I'd wager the average person on the street is a bit unclear on the specifics, too. Second, this is one of those areas where a picture really can be worth a thousand words -- or, barring that, it…

Scott Aaronson is explaining "Physics for Doofuses," and has started with electricity. He's got a nice breakdown of the basic quantities that you need to keep track of to understand electricity, leading up to Ohm's Law. He asks for a little help on this point, though: Well, as it turns out, the identities don't always hold. That they do in most cases of interest is just an empirical fact, called Ohm's Law. I suspect that much confusion could be eliminated in freshman physics classes, were it made clear that there's nothing obvious about this "Law": a new physical assumption is being…

It's been a while since I did a "Basic Concepts" post. They tend to take a good bit of effort, and things have been hectic enough at work that I haven't had the energy. To make up for the blizzard of basketball-related stuff over the last week (with more to come), here's a look at the concept of measurement. This one is almost more philosophy than physics, and there is a distinct possibility that I'll accidentally say something really stupid. The question of measurement in physics, particularly modern physics, is a very subtle and fascinating one, though, and it's worth a little discussion.…

Having talked about force and fields, it seems fairly natural to move on to talking about energy, next. Of course, it also would've made sense to talk about energy first, and then fields and forces. These are interlocking concepts. A concise one-sentence definition of energy might go something like: the energy content of an object is a measure of its ability to change its own motion, or the motion of another object. That's a little longer than the previous one-sentence descriptions, but I'm trying to avoid the recursion effect of the usual one-sentence definition, "Energy is ability to do…

In the initial "Basic Concepts" post, I discussed the concept of Force in physics. This time out, I'll be talking about fields, which is a much dicier proposition. Not only are fields considerably more abstract than forces, but I've never lectured on fields in general (specific instances of fields, yes, but not fields as abstract objects). For that matter, I've never taken a real field theory class. The chances of my saying something stupid about fields are exponentially greater than the chances of my saying something stupid about forces. In a certain sense, though, "Fields" is a good topic…

This is the first post I'm doing for the "Basic Concepts" series. When I asked for suggestions, I got a good long list of stuff, and it's hard to know quite where to start. I'm going to start with "Force," because physics as we know it more or less started with Isaac Newton, and Newton is best known for his work on forces. In fact, as-you-know-Bob, the SI unit of force is the "Newton," in ol' Isaac's honor. (I should note that this particular discussion is adapted from a lecture that I give in the introductory mechanics class, so there's also a "path of least resistance" argument for starting…